ABSTRACT

In this work, the effect of crystallographic orientations and the strengthening due to grain/twin boundaries were investigated by uniaxial compression of single- and bi-crystal micropillars of pure zirconium (Zr) with ≥99.9% purity. Micropillars fabricated using focused ion beam (FIB) milling were compressed using a flat punch tip in a nanoindenter to obtain stress–strain curves for individual orientations of Zr. Only near-basal-oriented samples were deformed by multiple slip, while samples with other orientations were deformed by a single slip. Bi-crystal samples had significantly higher flow stress than single-crystal samples – the increment in flow stress arising from grain boundaries being higher than that arising from twin boundaries. Our analysis shows that while twin-boundary strengthening can be explained based on a size effect according to the Hall-Petch equation, the higher strengthening effect of grain boundaries appears to arise from a combination of a sample-size effect as well as dislocation accumulation at boundaries.

抽象的

在这项工作中，通过单轴压缩纯度≥99.9％的纯锆（Zr）单晶和双晶微柱，研究了晶向和晶粒/孪晶边界引起的强化的影响。使用聚焦离子束（FIB）铣削制造的微柱在纳米压头中使用平冲头进行压缩，以获得Zr各个方向的应力-应变曲线。只有近基底取向的样品会因多次滑动而变形，而其他取向的样品会因一次滑动而变形。双晶样品的流变应力明显高于单晶样品–晶界引起的流变应力的增加高于晶界引起的流变应力的增加。